1. Field of the Invention
The invention relates to the defoamer formulations comprising organopolysiloxanes and to the use thereof in aqueous surfactant systems.
2. Description of the Related Art
In many liquid systems, more particularly aqueous systems, which include surface-active compounds either as wanted or else unwanted constituents, problems due to foaming may occur if these systems are brought into more or less intense contact with gaseous substances, as for example when gasifying waste waters, when intensively stirring liquids, in distillation, washing, or coloring operations, or during dispensing procedures.
Controlling this foam may be accomplished mechanically or through the use of defoamers. In this context, siloxane-based defoamers have proven themselves particularly useful.
Defoamers based on siloxanes are prepared according to U.S. Pat. No. 3,383,327 A, for example, by heating hydrophilic silica in polydimethylsiloxanes. Employing basic catalysts allows the activity of such defoamers to be improved (U.S. Pat. No. 3,560,401 A). An alternative is to disperse hydrophobized silica in a polydimethylsiloxane, in accordance with DE 29 25 722 A, for example. But the activity of the resulting defoamers is still capable of improvement. Accordingly U.S. Pat. No. 4,145,308 A, for example, describes a defoamer preparation which as well as a polydiorganosiloxane and silica also includes a copolymer composed of (CH3)3SiO1/2 units and SiO2 units. Copolymers composed of (CH3)3SiO1/2 and SiO2 units are also said to be advantageous in combination with siloxanes which carry long alkyl groups (U.S. Pat. No. 4,919,843 A).
The use of partly crosslinked polydimethylsiloxanes, which are in part already rubberlike, for boosting the defoamer effect has been known for some considerable time (U.S. Pat. No. 2,632,736 A). Such products may be prepared, for example, by radical crosslinking of polydimethylsiloxane (e.g., DE 3805661 A1, EP 273 448 A2). But these methods are very unspecific and yield products which are difficult to handle.
EP 163 541 A2 teaches the production of a defoamer preparation having improved long-term effect by catalytic reaction of trimethylsiloxy-terminated polydimethylsiloxanes, hydroxyl-terminated polydimethylsiloxanes, an alkoxysilane and/or siloxane, or a copolymer composed of (CH3)3SiO1/2 units and SiO2 units, and also a filler, in the presence of a catalyst. Catalysts referred to are bases or organometallic compounds.
The preparation of a defoamer by mixing hydrophobic silica with a polysiloxane that has been prepared by alkali-catalyzed reaction at temperatures of more than 120° C. from trimethylsilyl-terminated polydimethylsiloxanes, hydroxyl-terminated polydimethylsiloxanes, and a copolymer composed of (CH3)3SiO1/2 and SiO2 units is described by EP 217 501 A2. The intention thereby is to improve the activity of the defoamer at high concentrations of anionic surfactants.
A boost in effect is possible through addition of partly crosslinked siloxanes (EP 434 060 A2). Such partly crosslinked and branched structures are also possible through the reaction of terminally vinyl-containing siloxanes with Si—H functional siloxanes (EP 516 109 A1, DE 44 44 175 A1, DE 42 23 644 A1).
EP 434 060 A2, EP 516 109 A1, and DE 42 23 644 A1 describe branched polysiloxanes as constituents of defoamers which are obtained in a hydrosilylation reaction of terminally vinyl-containing siloxanes with Si—H functional siloxanes, the branched polysiloxanes therefore having structural units of the formula O2/2MeSi—CH2CH2—SiMe2O1/2.
Partly crosslinked and branched structures which are used in defoamer formulations are further accessible through reaction of compounds which have at least three aliphatic double bonds with Si—H-functionalized organopolysiloxanes (DE 10 200 40 52 421 A1, DE 10 200 50 36 748 A1).
U.S. Pat. No. 7,105,581 B1 describes antifoams based on siloxanes that comprise a branched polyether-polysiloxane copolymer as an additive. The copolymer added is a surfactant.
In strongly foaming, surfactant-rich systems, however, the defoamer formulations produced according to the prior art do not always exhibit sufficient activity or are difficult to handle on account of the high viscosity and/or the degree of crosslinking that is achieved.